Tuesday, April 30, 2013

Slowly but Surely

            Few pathogens inspire fear to the degree that prions do. As the culprit behind such mysterious diseases as mad cow disease and Familial Fatal Insomnia, prions are avoided at all costs. In December of 2003 more than 30 countries closed their borders to all beef imports from the United States because just one cow from the state of Washington tested positive for mad cow disease (1). But what are prions? And why do they evoke such aggressive responses?
            Prions are not viruses but rather a misfolded form of a particular protein, called prion protein (PrP).  This protein, whose function remains unclear, is found throughout the body of healthy individuals in its properly folded state, known as PrPC. When an individual is exposed to a prion, the misfolded form of PrP known as PrPSc, the prion can cause the normal protein to adopt its misfolded state. The normal PrPC is converted into the abnormal PrPSc, which can then go on to convert more healthy proteins into their pathogenic form. Eventually amyloid plaques of these abnormal proteins build up, mostly in neuronal tissue, causing transmissible spongiform encephalopathies, holes in the brain that continue to grow until the individual has passed away.
            Prion diseases are universally fatal and there is no currently approved treatment to slow their advance (P). Because these diseases occur due to a single misfolded protein, they are not reliant on a nucleic acid based entity for transmission, as is every other known transmissible disease. It is for this reason that prions are not susceptible to normal sterilization procedures, including high temperatures and UV radiation. Transmission can occur solely due to ingestion of infected neural tissue or, as more recently suggested, via inhalation of air droplets (2). Because there is no known treatment for prion diseases countries tend to go to relatively extreme measures to prevent prions from crossing their borders.
            However, new research suggests that the use of PrP antibodies, both prophylactically and after infection has taken root, might help slow prion disease progression (3, 4, 5, 6).  These antibodies bind to specific regions of the normal PrP protein, helping them resist conversion to their prion form (4). However, these have mostly involved in vitro studies, which do not necessarily mean that there are practical clinical uses for anti-PrP antibodies in treating prion diseases. One of the main hurdles to overcome is getting these antibodies to target tissues in the central nervous system at concentrations high enough to have an effect. In order to do this the blood brain barrier (BBB), which is normally impermeable to antibodies, must be overcome. In the past this has meant inserting the drugs directly into the brain of mouse models. However, it would be more suitable in human patients for a less invasive delivery method to be used, especially considering the possible transmission of prions that could occur during brain surgery.

Monday, April 29, 2013

A Virus Can Treat Cancer?

A chicken-killing virus? To treat cancer?

Ever thought a chicken-killing virus could be used to treat cancer? Probably not. But a recent study has discovered amazing potential in using Newcastle disease virus to kill prostate cancer cells. In what is known as oncolytic virotherapy, viruses like the one used in this recent study are implemented as tools to destroy cancer. Newcastle disease virus (NDV) is an avian paramyxovirus that infects wild and domestic bird species. It can cause flu-like symptoms and mild conjunctivitis in humans, but does not pose a significant threat to us. In addition to NDV being essentially non-pathogenic to humans, it can be used in cancer treatment strategies because it is an inherently tumor selective oncolytic virus. This potentially daunting description essentially translates to NDV’s ability to target and destroy cancer cells without posing a threat to healthy cells. In the recent study by Shobana et al. (2013), the authors investigated this virus’s potential for specifically killing human prostate cancer cells.
Newcastle disease virus

Why is this treatment so important?

Such an investigation has significant clinical implications, given that prostate cancer is the second leading cause of cancer-related deaths in the United States. To put things in perspective, almost 17% of men will develop prostate cancer at some point in their lives. Treatment of prostate cancer typically involves hormone therapy or chemotherapy, both of which have significant adverse side effects. Furthermore, current treatments for hormone-resistant prostate cancer only marginally increase survival and are often aimed at palliative, or pain management, care. Given the adverse effects and low effectiveness of the typical treatment approaches, there is much hope that we can begin to turn to oncolytic virotherapy as a novel approach to prostate cancer treatment. Using NDV as the vector in this therapy would alleviate patients from the often painful side effects of more standard cancer treatments. Although many issues are still associated with oncolytic virotherapy,  Shobana et al. (2013) present findings that make scientists hopeful such a treatment will soon have real clinical applications for treatment of what is now the second leading cause of cancer death in men.

Sunday, April 28, 2013

Rubella virus- Vaccinate your kids, Vaccinate your wife!

Rubella- an old enemy        
            Rubella virus, also known as German measles, is an acute viral infection that causes a rash and fever.  Typically, there are no major complications associated with rubella, as the disease lasts for three days, and causes no serious illness among children and young adults (1).  However, pregnant women who are exposed to the disease face a slew of complications (1).  German measles in pregnant women can result in damage to the fetus and potential birth defects, including mental retardation, deafness, cataracts, liver and spleen damage, as well as heart defects (1).  If a pregnant woman is infected with rubella, there is roughly a 20% chance that the fetus will be affected (1).

Rubella- people still get that?

            Due to a successful vaccination program, rubella incidences have significantly dropped in the past several decades.  Through proper protocol, all infants and unvaccinated adults receive two doses of the MMR (mumps, measles, and rubella) vaccine in order to build an immune defense against possible infection (1).  For a while, strong vaccination efforts were followed, resulting in a significant drop in cases of rubella.  However, in recent years, some parents have decided to not vaccinate their children against rubella.  While some feel that the disease is antiquated and there is no purpose in vaccination, others believe that there are potentially harmful effects associated with infancy vaccination.  As psychologists and neurologists attempt to search for the causes of newly emergent autism spectrum disorders, many fear that there may be some sort of correlation between vaccination and the onset of autism.  Although there is no significant scientific data to support such findings, not everyone blocks out potentially false information.  As a result, some childhood diseases, such as rubella, have made a “comeback” and are of concern to children and pregnant women.

Beijing- a rubella case study

            Recently, Chinese epidemiologists have monitored the outbreaks of rubella in Beijing from 2007-2011.  Unlike in the United States, the rubella vaccine was not widely distributed in Beijing until 1995.  Before this, there were high levels of rubella among the residential population, and commuters into the city (floating population).  After the vaccine became widely available, the reported cases of rubella among both the permanent and floating populations drastically lowered.  Through statistical analysis, epidemiologists found that the overall rate in rubella infection has remained relatively stagnant from 2007-2011, but slightly higher than initially after vaccination began.  They also founds that the ratio between floating population incidences and residential incidences has increased.  In some of the years, such as 2007, the rate for the floater population was more than three times greater than that of the residential population. 

Is the flu shot worth it?

Have you ever received a flu shot (thinking you'd get through flu season unscathed), only to come down with the characteristic fever, sore throat, and lethargy along with everyone else? Why did you still get the flu? Or, has your doctor ever recommended the flu shot with the disclaimer that this season's flu shot may only serve to lessen symptoms, and that you shouldn't count on being fully immune? Don't blame the doctors, and don't blame the scientists: as it turns out, we are in an ever 'one-step-behind' race with influenza.

The ability of the flu to rapidly mutate is the reason behind our inability to eliminate the occasional but consistent flu pandemic; with a high error rate due to RNA polymerase's lack of endonuclease proofreading ability (the flu is an RNA virus), everything in the flu genome mutates at rates higher than our own DNA, and many other viruses (1). For a similar host immune-evasion reason, HIV has proven extremely difficult to eradicate. While HIV antiretroviral treatments have successfully targeted the virus at a multitude of steps in its replication cycle (2), virtually indefinitely preventing progression to AIDS, it is a latent virus, and so cessation of medication leads to resumption of particle manufacture. Thankfully, influenza is an acute virus, and so as quickly as it comes, it goes. However, symptoms of the flu can be very taxing on the human body, ranging from high fevers to nasal discharge/sneezing/general respiratory problems (3) to sometimes unrecoverable weight loss (at least in ferret models); in some cases, vulnerable groups may even die if infected. We would hope that the vaccines that we create to protect ourselves from this ravaging bug would be highly successful in attenuating the severity of these symptoms, and even better, prevent us from acquiring the virus altogether. However, the ability of the flu to evade our immune systems through mutation of its immunogenic properties makes creation of the perfect flu shot, a long shot.

Influenza has two surface proteins, hemagglutinin (HA) and neuraminidase (NA) (3); flu strains are classified according to the specific combination of these surface molecules. For example, the H1N1 strain contains H1 and N1 isotypes of HA and NA respectively. Since HA has been shown to play an important role in the flu virus's ability to enter a cell, a hosts ability to create antibodies against a specific HA molecule often correlates positively with immunity to that specific strain (or homologous strains). Thus, in creating a vaccine, it is reasonable to use an attenuated, recent flu strain isolate in an attempt to stimulate host HA antibody production for immunity against similar/future strains. However, rapid mutation of the virus quickly out-dates our vaccines, and sometimes we are just unable to keep up.

Thursday, April 25, 2013

Why haven’t we found a cure for HIV?

     In 1983 the human immunodeficiency virus (HIV) was first isolated and suggested as the root cause of acquired immune deficiency syndrome (AIDS), a universally fatal condition thanks to various opportunistic diseases that take advantage of the sufferers weakened immune system (1). Today HIV is one of the most intensely researched viruses in the world and new drugs are constantly being developed to minimize its effects in HIV+ patients. Yet despite sophisticated cocktails of these drugs that are administered during the most popular treatment for HIV infection, highly active antiretroviral therapy (HAART), we still have not managed to develop a therapeutic strategy to fully eradicate the virus from those infected with it.

     The reason a cure for HIV has been so difficult to obtain has to do with the virus’s latent reservoir. Most cells that become infected with HIV start producing infectious viruses within a few days. And they do this at a high enough rate that the cell eventually dies, either directly due to the viral replication itself or indirectly due to the host’s immune system. These cells die off and are no longer a threat for producing more viruses. A cell involved in the HIV latent reservoir, however, only produces viruses at a low rate or not at all. It can remain dormant, evading the host’s immune system while still containing the HIV genome and, therefore, the ability to produce infective HIV viruses. Recent research has suggested that memory T cells, which are involved in the mechanism that allows the immune system to remember pathogens after infection has cleared, make up the largest proportion of the HIV latent reservoir (P,2). The long-lived nature of this cell type means that it would take an exceedingly long time to wait for each of these proviral cells to die. Recent modeling suggests it could take up to 70 years (3).

     Because so many successful antiretrovirals have been developed, patients adhering to HAART can delay the onset of AIDS indefinitely (P). These drugs are very good at preventing any HIV viruses that persist in the patients bloodstream from infecting new CD4+ T-cells, the viruses target cell type. However, once taken off HAART, these patients start shedding new viruses and progress rapidly to AIDS. Therefore, HAART must be a lifelong treatment, one that is very expensive and very difficult to keep up with. The reason HAART does not fully eradicate HIV is because the cells of the latent reservoir still contain the HIV genome, which enables those cells to manufacture infectious viruses, which are detected in the individuals blood. If the patient is fully adhering to HAART these viruses simply degrade and do not infect new cells. But if the patient is taken off HAART these viruses can infect new cells, which can then go on to shed more viruses.

Wednesday, April 24, 2013

An Emerging Influenza Vaccine

            Throughout history, the influenza virus has proven to be highly problematic for human beings.  Various epidemics have spread across the globe and taken many lives, including the recent avian flu (H5N1) and swine flu (H1N1).  While the virus itself does cause a lot of harm, it is often pneumonia caused by Staphylococcus aureus (S. aureus), which results from the influenza infection, that often proves to be fatal (1).  Virologists have been looking for a vaccine that would help not only to prevent influenza infection, but also to deter S. aureus infection.  In their journal article, Dai et al. explain how they found a conserved section of the protein HA which can be made into a vaccine and coupled with the bacterial antigen Ag85A to do just that.

            The HA protein in Influenza A Virus (IAV) holds domains necessary for viral attachment to host cells.  To activate this protein, the virus cleaves it into two domains: HA1 and HA2.  The host often deploys an immune response that targets antibodies to the HA protein, which prevents IAV virions from attaching to the host cells (2).  While this is temporarily affective, IAV tends to evolve very rapidly, so vaccines geared towards the HA protein become outdated very quickly (3).  However, the HA2 domain has been seen to remain highly conserved over virus generations, and the majority of the mutations can be attributed to the HA1 region.  Therefore, it seems reasonable that if antibodies were made to target the HA2 region specifically, then they would be able to be effective for longer periods of time (4).

            Ag85A is an antigen secreted by the bacteria Mycobacterium tuberculosis (M. tuberculosis).  As a vaccine, Ag85A was known to increase the production of T helper 1 (TH1) cytokine responses to M. tuberculosis (5), which in turn lead to an increase in the expression of toll-like receptor 2 (TLR2).  TLR2 recognizes molecules specific to Staphylococcus species and activates immune responses to them (6).  Therefore, Ag85A could act as a vaccine for S. aureus.  Dai et al. hypothesized that combining the HA2 domain of the HA protein and Ag85A into a single vaccine would create both an effective antibody response to IAV and antibacterial response to S. aureus, preventing both influenza and the potentially lethal pneumonia that tends to follow.

Monday, April 22, 2013

Who's responsible?

Did you know that termites are actually incapable of consuming plant material on their own? It's true: they rely on a host of bacterial helpers that reside in their gut to break down their food for them. In turn, the bacteria depend on the host for this supply of raw energy (3). This is a classic example of mutualistic symbiosis, where two organisms benefit from each others' presence (in nature, this can be in the form of chemical aid as mentioned above, or may come in some other form, like protection/shelter).

Why should we care? Well, to better understand cause and effect relationships in nature, we need to be aware of all the components that are playing a role. For example, imagine if there was such a scenario where the flu virus actually infected and resided within helpful bacteria that lived in our lungs, and not us directly (and the cause of sickness were due to the death of these bacteria). If this imaginary flu-carrying bacterium turned out to be unable to survive on skin and other common surfaces but ultra-resilient as an airborne pathogen, then our whole idea of flu transmission would be wrong, and health policy would need be reformed; people would be far less concerned with washing their hands and sanitizing surfaces, and would start wearing masks. To take full advantage of our surroundings, we need to fully understand our surroundings.

Such may be the case with the Tomato yellow leaf curl virus (TYLCV). As its name might suggest, the acquisition of this disease by tomatoes causes a curling/shriveling of the leaf, a yellow discoloration, stunting of plant growth, and more (2), and can result in complete loss of tomato crop; this, consequently, leads to disastrous economical impacts. In a study by Su et al., it was found that the incidence of TYLCV infection correlated strongly with the presence of a bacterial symbiont of whitefly Bemisia tabaci. B. tabaci is known to transmit this virus, but what we did not know previously is that symbiont Hamiltonella is likely responsible for its intense transmission.

Identifying a deadly foodborne bacteria: What’s virus got to do with it?

Image Source

--A recent study uses a new approach to investigate the shiga toxin producing bacteria responsible for a serious disease outbreak in Germany in 2011. The real culprits behind the outbreak are the viruses that carry the gene for shiga toxin and transfer it to otherwise harmless bacteria  --

            What’s harder than finding a needle in a haystack? Finding the bacterial genome you’re looking for in a diarrhea sample. A recent study published on April 10, 2013 in the Journal of the American Medical Associaton (JAMA) made this task seem relatively easy. The bacteria being searched for was a  rare shiga toxin producing bacteria that causes bloody diarrhea and other severe complications in humans upon infection. This study was done by an international team of researchers coordinated by Mark J. Pallen who recently became the head of Warwick Medical School’s new Division of Microbiology and Infection. The bacterial strain that caused an outbreak in Germany was especially rare making it hard to identify. Because of this, researchers employed a new method to identify the genome sequence of this highly pathogenic bacteria. Their method of detection was to sequence all the genetic material present in fecal samples from patients with diarrhea during the outbreak and sort through this genetic information to find the sequence of the disease causing strain.

            The source of the outbreak in Germany during the summer of 2011 is believed to be from the consumpton of raw sprouts contaminated with the dangerous bacteria strain (2). This outbreak affected thousands of people in a wealthy, modern, industrialized society, causing more than 50 deaths (4). In times like this, quick identification of the causative pathogen (in this case a shiga toxin producing bacterial strain) is critical for the management of the outbreak. Traditionally, the standard for identifying pathogens in clinical samples is to isolate the disease causing bacteria from other microbiota in the samples and then sequence it once it is in pure culture. This study's approach is different becuase they directly sequenced the mixed communities of bacteria and anything else present within the feces sample and then analyzed the sequence data to find the disease causing bacteria. The sequencing of mixed microbial communities is called metagenomics and allows identification independent of laboratory isolation and culture of the causative bacteria.

Sunday, April 21, 2013

Nipah Virus: a real life Contagion?

A newly emergent, deadly virus

            Throughout the last fifteen years, a highly fatal virus has emerged.  Since its first discovery in 1998, Nipah virus has infected nearly 500 people throughout Asia, and produced a mortality rate greater than 50% (1).  Nipah virus can be spread from either human-animal or human-human contact.  During the first outbreak of Nipah, transmission occurred primarily via respiratory droplets from infected pigs in Malaysia (2).  On the other hand, some of the outbreaks in India and Bangladesh were most likely due to contact with fruit bat saliva or urine (1).  In addition, some of the more recent cases of Nipah were transmitted directly from person to person, with many of the infections occurring in a hospital setting (1).  At first, Nipah virus symptoms resemble those of the flu, as many patients report headaches, muscle pains, vomiting, and a sore throat (1).  However, as the disease progresses, people experience encephalitis, and possible respiratory illness (1).  In serious cases, Nipah can lead to coma and death (1). There currently are no vaccines or treatment options for Nipah.

            Nipah virus is a member of the Paramyxoviridae family (2).  It is closely related to the Hendra virus, which causes similar respiratory and neurological symptoms (3).  Nipah virus is a (-) sense, single-stranded RNA virus that contains a nonsegmented genome (2).  Because Nipah is such a fatal virus, and there are no vaccines or treatment options available, there is little known about it.  All research involving Nipah must be completed at BSL-4 facilities containing the highest possible levels of security and safety.  Recently, researchers at the Institute of Virology, Philipps University of Marburg, Germany investigated how Nipah virus enters and exits an infected epithelial cell.   Although researchers have clinically proven that Nipah infects epithelial cells in the respiratory and urinal tracts, the mechanisms behind this are largely unknown.

Researching the unknown Nipah virus

            The first major objective of this study was to observe the mechanisms of Nipah virus (NiV) entry into a polarized epithelial cell.  To start, the researchers observed the distribution of the NiV entry receptors on the cells.  Specifically, they looked at the ephrin receptor expressions on polarized kidney epithelial cells (MDCK).  The researchers found an even distribution of ephrin throughout the apical and basolateral surfaces of the cell.  Then, MDCK cells were selectively infected to either the apical or basal filter chamber; and immunostained for presence of NiV in the cell.  As expected, NiV was able to infect the MDCK cells regardless of the surface domain.  Thus, NiV entry was found to be bipolar.

Thursday, April 4, 2013

Bacterial Infection? ...Have a dose of virus.

            When you go to a hospital, you typically expect it to make you better, not get you sicker. Unfortunately, hospitals are filled with bacteria, many of which ‘prey’ on patients with weakened immune systems and preexisting health issues. One such bacterium is klebsiella, a genus of Enterobacteriaceae. This bacteria is estimated to cause nearly 8% of all nosocomial (hospital-acquired) infections each year (Podschun, 1998). Klebsiella pneumoniae is normally found growing in places such as the mouth and on skin, but it can create health issues if it enters the lungs, causing inflammation, hemorrhaging, and necrosis of lung tissue. It is especially dangerous if bacteria have developed antibiotic resistance, as an increasing number of hospital-acquired infections have done.
            This resistance is coded for in plasmids (small, circular, transferrable bits of DNA) that the bacteria pick up. A common protein that causes antibiotic resistance is beta-lactamase. This enzyme, breaks open the beta-lactam ring in antibiotic molecules containing this structure, thereby deactivating them. Penicillin is one such beta-lactam-based antibiotic. It is widely used to treat bacterial infections, and resistant bacterial strains are a large reason for concern. While there are other antibiotics that can be used, some of these bacteria have extended-spectrum beta-lactamase genes, which makes them even more efficient at denaturing a wider range of beta-lactam antibiotics. In poorer areas, where less common antibiotics are harder to come by, this is even more of an issue. In 2003, over half of the antibiotics in use were beta-lactam compounds (Elander, 2003).
            These infections add time to hospital stays. Not only is this an inconvenience, but it is also an economic drain on the hospitalized individual. These types of infection are also prominent in intensive care units, where patients are already suffering from depressed immune systems, and an added infection without the help of antibiotics can kill a patient.
            For this reason, the search for alternate antimicrobials is a high priority. Bacteriophages (viruses that only infect bacteria) hold great promise in this area, but to be effective, they must be able to infect a wide host of bacteria. There are four types of host resistance mechanisms to bacteriophage infection: adsorption inhibition, blocking of DNA injection, restriction-modification, and abortive infection (Weinbauer, 2004). The host restriction system is one of the best-studied parts of this system. In “Characterizing the biology of novel lytic bacteriophages infecting multidrug resistant Klebsiella pneumoniae,” Kesik-Szeloch et al. culture and screen a number of bacteriophages for the pathogenicity in Klebsiella, and their abilities to resist host restriction-modification mechanisms.